This invention generally relates to the provision of tamper-evident features in reclosable packaging. In particular, the invention relates to tamper-evident features for use in reclosable packaging of a type having a slider-operated string zipper.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened.
Reclosable bags typically comprise a receptacle having a mouth with a zipper for opening and closing the mouth. In recent years, many zippers have been designed to operate with a slider mounted thereto. As the slider is moved in an opening direction, the slider causes the zipper sections it passes over to open. Conversely, as the slider is moved in a closing direction, the slider causes the zipper sections it passes over to close. Typically, a zipper for a reclosable bag includes a pair of interengageable profiled closure strips that are joined at opposite ends of the bag mouth. The profiles of interengageable plastic zipper strips can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, interlocking ball-shaped closure elements, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interengageable zipper profiles before causing those profiles to engage.
In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
In the past, many interlocking closure strips were formed integrally with the bag making film, for example, by extruding the bag making film with the closure strips formed on the film. Such constructions, however, were limited by the conditions required to extrude both the film and zipper together. To avoid such limitations, many bag designs entail separate extrusion of the closure strips, which are subsequently joined to the bag-making film, for example, by conduction heat sealing. These separate closure strips typically have flanges extending therefrom in such a way that the flanges can be joined to bag-making film in order to attach the closure strips to the film. Many previous slider-operated, separately extruded zippers used flange-type constructions.
An alternative zipper design is the so-called flangeless or string zipper, which has substantially no flange portion above or below the interengageable closure profiles. In the case of a string zipper, the bag-making film is joined to the backs of the bases of the closure strips. String zippers can be produced at much greater speeds, allow much greater footage to be wound on a spool, thereby requiring less set-up time, and use less material than flanged zippers, enabling a substantial reduction in the cost of manufacture and processing.
Various additions to reclosable bags have been made to provide tamper-evident seals or indicators that will reveal when the bag has been opened or otherwise tampered with prior to purchase by the consumer. It is known to provide a reclosable package construction that is designed to undergo some permanent change in the package appearance when the package is opened for the first time. For example, it is known to provide a reclosable package with a tamper-evident, non-reclosable peel seal that gives a positive indication of having been broken when a package is first opened. It is also known to shroud the zipper (with or without slider) inside an enclosed header on the top of the bag. Another type of tamper-evident feature is the provision of a membrane on the product side of the zipper that partitions the interior volume in an airtight manner.
U.S. Pat. No. 6,347,885 discloses a reclosable package having a slider-operated flanged zipper shrouded by a tamper-evident structure. An opening in one or both walls of the tamper-evident structure provides a view of the slider. Optionally, the openings may encircle the slider, with the perimeters of the openings serving to block movement of the slider in the opening direction. Additional tamper-evident structure may be provided in the form of a peel seal (between the bag panels or between the zipper flanges) or in the form of a web that, in effect, connects the zipper flanges to form a membrane, each of these optional features serving to block access to the product even after the zipper has been opened. U.S. Pat. No. 6,347,885 is silent regarding providing tamper-evident features on a reclosable package having a slider-operated string (i.e., flangeless) zipper.
There is a need for new designs for slider-operated string-zippered reclosable packages with tamper-evident features that can be manufactured at low cost.